updated 7:00 p.m. ET Nov. 5, 2008

PITTSBURGH - Ben Roethlisberger rested his sore right shoulder on Wednesday, although his latest tests showed no additional damage, The Pittsburgh Steelers might not know until late in the week if he can play Sunday against Indianapolis.

Byron Leftwich, who came off the bench to lead two key second-half touchdown drives against the Redskins on Monday night, practiced with the regulars and said he’s ready to play if needed.

“It really depends on where he (Roethlisberger) is at the end of the week and if he is capable of being Ben,” coach Mike Tomlin said. “If he’s not, we will go with Byron.”

Roethlisberger’s MRI exam on Tuesday “is very similar (to his previous one), but it is not the same as it has been,” Tomlin said.

Roethlisberger’s throwing shoulder was slightly separated while he was sacked by Houston’s Mario Williams during the Sept. 7 opener. He aggravated the injury on a 1-yard touchdown run late in the first half of the Steelers’ 23-6 win Monday night and did not play again.

“I think what happened was it was getting better, then it went back to square one,” said Roethlisberger, although he is optimistic about playing. “I played through it before and we’ll do it again.”

Resting a week might not necessarily benefit Roethlisberger, Tomlin said, even if sitting out would temporarily alleviate the stress placed on the shoulder in games. Tomlin suggested the shoulder might not be 100 percent until after the season ends.

“I don’t think he is any more susceptible to injury than if he was given a clean bill of health,” Tomlin said. “I think it is one of those injuries that is going to be better in the offseason, like a lot of (the injuries) those guys have down in the locker room.”

Despite the nagging injury, Roethlisberger has thrown 10 touchdown passes while guiding the division-leading Steelers to a 6-2 record.

Leftwich, if he is needed to play, knows the Colts well. He was Jacksonville’s quarterback from 2003-06, going 2-4 against Indianapolis while completing 100 of 155 passes for 1,134 yards, six touchdowns and three interceptions.

“It’s two different teams, two different organizations, but we did play each other twice a year,” Leftwich said. “You knew each other pretty well. But I don’t think that, because I’ve had some success in the past, it will automatically carry over.”

One problem for Leftwich is getting comfortable with a Steelers offense he only began learning two weeks into training camp. He didn’t sign with them until Charlie Batch broke his collarbone Aug. 8.

Another problem: Leftwich found himself calling plays Monday night he hasn’t run with the regulars in practice.

Leftwich takes most of the snaps in practice when Roethlisberger rests but, Leftwich said, “The only problem is that none of those plays have been called in a game yet.”

Switching between Roethlisberger and Leftwich also takes some adjustment for the receivers.

The more-mobile Roethlisberger occasionally swings out of the pocket to improvise a play and avoid a sack, one reason he tends to hold onto the ball longer. Leftwich mostly stays in the pocket but delivers a harder pass, and he also gets rid of the ball faster.

“Whoever is in the game, either Ben or Byron, we feel confident that both quarterbacks can go out there and get the job done,” Hines Ward said. “We’re in a fortunate situation to have two quarterbacks like that. A lot of teams don’t really have a backup as capable as Byron.”

Leftwich won’t start debating in his mind whether he will play, especially because he might not know until Friday — or later. So he always prepares himself during practice as if he will play.

“I need to go out there and play well enough for us to win,” he said.

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